[Haskell-cafe] How to cabal fetch mtl==2.0.0.0?

[Bas van Dijk]

On Thu, Nov 25, 2010 at 2:52 AM, Iain Alexander <ia at stryx.demon.co.uk> wrote:
> <log>
> F:\Util\Haskell>cabal fetch mtl==2.0.0.0
> Resolving dependencies...
> cabal: internal error: could not construct a valid install plan.
> The proposed (invalid) plan contained the following problems:
> The following packages are involved in a dependency cycle transformers-0.2.2.0,
> special-functors-1.0, mtl-2.0.0.0
>
> F:\Util\Haskell>cabal -V
> cabal-install version 0.8.2
> using version 1.8.0.2 of the Cabal library
> </log>
>
> Could someone please remind me of the correct incantation to make this work.
>
> (I observe that transformers-0.1.4.0 optionally (by cabal flag) depends on
> special-functors, and special-functors-1.0 depends on mtl.  So given that mtl-2
> no doubt depends on transformers, I can see the potential for confusion, but
> there presumably must be a way of breaking the (apparent) loop.)
>
> TIA,
> Iain.
> --
> Iain Alexander      ia at stryx.demon.co.uk
>
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Maybe it helps if special-functors gets an upper bound on its mtl
dependency: mtl < 2.

BTW what is you ghc --version?

Because I have no problems fetching mtl-2:

$ ghc --version
The Glorious Glasgow Haskell Compilation System, version 6.12.1

$ cabal --version
cabal-install version 0.8.0
using version 1.8.0.2 of the Cabal library

$ cabal fetch mtl==2.0.0.0
Resolving dependencies...
Downloading mtl-2.0.0.0...

Regards,

Bas